Devices for the delivery of medicament in an automatic way e.g. auto-injectors, are known as convenient and safe aids for patients to administrate various drugs themselves. For safety reasons, many devices for the delivery of medicament include covers and other devices that protect users before and after use, for example, from an injection needle. Although different devices for the delivery of medicament vary in their total feature sets, they all have a mechanism that delivers the contents of a preloaded, prefilled container automatically, i.e., without requiring a person to manually force the contents within a container through a delivery member e.g. a needle, a nozzle, into the patient.
One problem associated with self-administration of medicament with injectors that perform the injection automatically is how the user could know when the injection is completed and it is safe to remove the injector from the injection site. This is a non-negliable problem because many drugs need to be injected in rather precise doses and if the injector is removed to soon, a part of the dose may be expelled outside the body of the patient. It could also be that the dose needs to be injected at a certain depth in the skin of the patient, and if the injector is removed prematurely a part of the dose may be injected into the skin during withdrawal, i.e. at lesser depths.
There have been certain attempts to alert or indicate to the user when the injection is completed. U.S. Pat. No. 6,221,046 describes an injection device having an “end of injection click” including an extension on a flexible tab of a dose dial mechanism. The tab with the extension falls into a groove in the housing, causing an audible click at the end of injection. US 2004/0097883 discloses a similar end of injection click solution.
Other solutions include indicators that are moved during injection. One such device is disclosed in US 2005/0277886 where an indicator is connected to an intermediate part in an injector such that the indicator only moves or is visible, during a second distance of a total movement distance of a plunger rod, where the total movement distance includes a first penetration distance and second injection distance.
The above solutions are not optimal in all aspects. The audio information may be lost if the device is used in a noisy environment and the click of a tab falling into a groove may not be heard even in rather quite environments. The mechanical indicator solution entails a number of extra components which makes the injector more complicated and more expensive. Further the indicator according to US 2005/0277886 is visible on the side of the injector which is not an ideal place since the user has to be certain when using the device that the hand grip does nor cover the indicator.